Manufacturing process, tool stand, and drill bit

ABSTRACT

A drill bit includes a drill bit head, a multi-strand helix made up of three or more helix ribs, and a shank end along a drill bit axis. The multi-strand helix is made up of a conveyance area, a helix gradient, and a pitch. The helix ribs extend parallel to the drill bit axis in a first area adjacent to the drill bit head and a second area adjacent to the shank end.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of prior U.S. application Ser. No.16/062,537, filed Jun. 14, 2018, which claims the priority ofInternational Application No. PCT/EP2016/079815, filed Dec. 6, 2016, andEuropean Patent Document No. 15200036.0, filed Dec. 15, 2015, thedisclosures of which are expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention involves a production method for drill bits plus adrill bit and a tool stand for carrying out a production method for adrill bit.

The inventive production method for a drill bit with a helix has thefollowing steps: cold reshaping of a rod-shaped blank to form asemifinished product with three or more rectilinear longitudinal ribsextending along the longitudinal axis of the semifinished product;introducing the longitudinal ribs of the semifinished product in a firstdie and a second die in the working direction, whereby the first diebears against the longitudinal ribs in the direction of rotation aroundthe longitudinal axis and the second die bears against the longitudinalribs counter to the direction of rotation; pivoting the first die in thedirection of rotation in relation to the second die in order to twistthe longitudinal ribs between the first die and the second die; pullingthe longitudinal ribs of the semifinished product through the pivotedfirst die and the second die counter to the working direction in orderto twist the longitudinal ribs; and attaching a drill head to the backend in the working direction.

The inventive process makes a high level of automation possible whenmanufacturing drill helixes of any length and with a variable helixgradient.

An inventive tool stand for producing a helix for a drill bit has afirst die and a second die arranged one after the other in the workingdirection on a working axis. The first die has a star-shaped hollowcross section on the front side that faces away from the second die thatcorresponds to the inverse shape of the cross section of the helix ofthe drill bit. The second die has a star-shaped hollow cross sectionthat corresponds to the inverse shape of the cross section of the helixof the drill bit. A pivoting drive can pivot the first die in relationto the second die in a basic position in which the star-shaped hollowcross section of the front side of the first die and the star-shapedhollow cross section of the second die have the same orientation. Thepivoting drive can then pivot the first die from the basic positionaround a pivoting angle in the direction of rotation. An axial drive canpull a semifinished product out of the first die and the second diealong the working axis.

In a preferred embodiment, the hollow cross section of the first dieincreases in size longitudinal to the working direction—at least counterto the direction of rotation. The fact that the cross section increasesin size allows the shaping process of the first die to proceed withgreater stability with a longer length, i.e., the dimension along theworking axis.

The following description explains the invention on the basis ofembodiment examples and Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 : a drill bit;

FIG. 2 : a cross section through a conveyance area of the drill bit atlevel II-II;

FIG. 3 : a cross section through an attachment area of the drill bit atlevel III-III;

FIG. 4 : a cross section through a discharge area of the drill bit atlevel IV-IV;

FIG. 5 : a schematic diagram of the process of reworking a blank to forma semifinished product;

FIG. 6 : a cross section through the semifinished product at levelVI-VI;

FIG. 7 : a cross section through a roller stand at level VII-VII;

FIG. 8 : a schematic diagram of the process of reworking a semifinishedproduct to form a helix;

FIG. 9 : a reshaping die;

FIG. 10 : a supporting die;

FIG. 11 : a front side of the reforming die;

FIG. 12 : a back side of the reforming die;

FIG. 13 : a cross section through the reshaping die at level XIII-XIII;

FIG. 14 : a front side of the supporting die; and

FIG. 15 : a section through the supporting die at level XV-XV.

DETAILED DESCRIPTION OF THE DRAWINGS

Unless otherwise indicated, elements that are identical or have the samefunction are identified using the same reference numbers in the Figuresshown.

FIG. 1 shows a sample drill bit 1. The drill bit 1 has a drill head 2, ahelix 3, and a shank end 4. For example, the drill bit 1 is designed forremoving mineral materials, e.g., reinforced concrete. During operation,the drill bit 1 is spun in the direction of rotation 5 around itslongitudinal axis 6 (drill bit axis). To do this, the drill bit 1 can beinserted into a handheld power tool that has a corresponding rotarydrive. A hammer mechanism of the handheld power tool periodicallystrikes the free end 7 of the shank end 4. The shock wave of the impactspasses through the helix 3 in the impact direction 8 to the drill head2. The drill head 2 shatters the material. For one thing, the rotarymotion ensures that the drill head 2 strikes the base in differentpositions, resulting in a bore hole that is evenly formed; for another,the helix 3 causes the drill cuttings to be carried away.

The drill head 2 in the example has four chisel edges 9. The chiseledges 9 come together at a tip 10 on the drill bit axis 6. The tip 10 ispreferably the highest point in the impact direction 8 and therefore iswhat first comes into contact with the material. The chisel edges 9 canrise in a radial direction from the outside to the drill bit axis 6along the impact direction 8. The chisel edges 9 are all orientedtowards the impact direction 8. The chisel edges 9 each consist of aleading facet that moves in the direction of rotation and a followingfacet, both of which are oriented in the impact direction 8. The twofacets are inclined towards each other; the top angle of the chisel edge9 is greater than 45 degrees, preferably greater than 60 degrees, andless than 120 degrees. The chisel edges 9 can all be designed the same,or each pair can be different from each other. The drill bit head 2 hasfour break-off edges 11 that extend parallel to the drill bit axis 6.The break-off edges 11 merge with the chisel edges 9. The break-offedges 11 define the diameter of the drill bit head 2. The number ofchisel edges 9 and break-off edges 11 can be selected depending on thediameter of the drill bit 1. For example, a drill bit 1 that has a drillbit head 2 with a small diameter can have two chisel edges 9, while adrill bit head 2 with a large diameter can have more than four chiseledges 9 and a corresponding number of break-off edges 11.

The drill bit head 2 is preferably made of a sintered material,specifically tungsten carbide. The chisel edges 9 and the break-offedges 11 are preferably joined together monolithically, specificallywithout a joint zone.

For example, the helix 3 of the drill bit 1 has four helix ribs 12. Thenumber of helix ribs 12 is preferably the same as the number of chiseledges 9. The helix ribs 12 extend along the drill bit axis 6 andmultiple times around this drill bit axis 6. The helix ribs 12 form acylindrical envelope 13 when the drill bit 1 spins. Adjoining helix ribs12 each have a helix groove 14 between them that is regarded asgeometrically bordered by the envelope 13 in a radial direction. Thedrill cuttings are transported in the helix grooves 14 by the helix ribs12 along the drill bit axis 6.

The helix 3 has different sections along the drill bit axis 6 that havevarious gradients for the helix ribs 12 in order to handle differentrequirements. A conveyance area 15 is the dominant section and is forconveying the drill cuttings. The conveyance area 15 typically extendsalong more than 80% of the length of the helix 3. The conveyance area 15can be right next to the drill bit head 2; alternatively, there can bean attachment area 16 between the drill bit head 2 and the conveyancearea 15 that is designed for the special requirements for attaching thedrill bit head 2 to the helix 3. The helix 3 ends with a discharge area17 at the end 7 pointed towards its shank end 4. The discharge area 17merges with the cylindrical shaft 18 of the shank end 4.

There is a helix gradient 19 of the helix ribs 12 in the conveyance area15; in other words, the helix ribs 12 are sloped in comparison to alevel perpendicular to the drill bit axis 6, ranging from 35 degrees to70 degrees. The helix gradient 19 of the helix ribs 12 is preferablyconstant along the entire conveyance range 15. The constant helixgradient 19 ensures that the drill cuttings are transported uniformly inthe helix 3. The constant helix gradient 19 results in a constant pitch20 of the helix 3. In an alternative design, the helix gradient 19 andthe pitch 20 can increase in the impact direction 8. Along the drill bitaxis 6 in the conveyance area 15, the helix 3 has a cross section (FIG.2 ) that remains uniform and spins continuously around the drill bitaxis 6. The cross section can be described by the helix diameter 21, acore diameter 22, the height of the helix ribs 12 and the depth 23 ofthe helix grooves 14, the average thickness 24 of the helix ribs 12, andthe average width 25 of the helix grooves 14, among othercharacteristics. The helix diameter 21 is the diameter of the drill bit1 or the envelope 13 of the helix 3, i.e., the smallest hollow cylinderin which the helix 3 can be spun around its drill bit axis 6. The corediameter 22 is the diameter of the largest circle that can fitcompletely in the cross section of the helix 3. The average thickness 24and the average width 25 can be determined halfway along the helix ribs12, for example. The core diameter 22, the height of the helix ribs 12,and the depth 23 of the helix grooves 14 remain constant along theentire conveyance area 15. Preferably, the average thickness 24 of thehelix ribs 12 and the average area 25 of the helix grooves 14 remainconstant along the entire conveyance area 15 as well.

In the sample drill bit 1 shown, the conveyance area 15 merges with theattachment area 16 in the impact direction 8. The drill bit head 2 issoldered or welded preferably onto the level end surface of theattachment area 16. The helix gradient 19 constantly increases in theattachment area 16 in the direction of the drill bit head 2. The helixgradient 19 preferably transitions to an orientation parallel to thedrill bit axis 6; in other words, the helix gradient 19 reaches 90degrees. The cross section of the helix 3 in the attachment area 16 canremain constant along its entire length (shown enlarged in FIG. 3 ).Preferably, the cross section of the attachment area 16 is congruentwith the cross section in the conveyance area 15. In particular, thecore diameter 22, the height of the helix ribs 12, and the depth 23 ofthe helix grooves 14 preferably remain the same. The surfaces of thehelix ribs 12 and the helix grooves 14 are smooth—in particular, theylack the roughness and scoring typical of cutting processes.

The transition from the helix gradient 19 in the conveyance area 15 tothe parallel orientation at the drill bit head 2 is continuous andpreferably with a uniform rate of change in the helix gradient 19 alongthe impact direction 8. The helix gradient 19 preferably increases inthe range of between 0.5 degrees and 2 degrees for every degree that thehelix rib 12 winds around the drill bit axis 6. The rate of change isminimal and constant throughout; the helix 3 does not exhibit any pointsor otherwise abrupt changes in the helix gradient 19.

In the discharge area 17 of the helix 3, the helix ribs 12 transitionfrom the conveyance area 15 to the cylindrical shank end 4. The helixgradient 19 preferably increases continuously in the discharge area 17until the helix ribs 12 extend parallel to the drill bit axis 6. Thecross section of the helix 3 can remain the same until the helix ribs 12are oriented parallel to the drill bit axis 6 (shown enlarged in FIG. 4). Then the cross section changes constantly counter to the impactdirection 8 to form a circle with the diameter 26 of the shank end 4,i.e., the cross section of the shank end 4. The helix ribs 12 becomeflatter and have shrinking radial dimensions; the helix grooves 14become flatter and increase in a radial direction.

The transition from the helix gradient 19 in the conveyance area 15 tothe parallel orientation at the discharge area 17 is continuous andpreferably with a uniform rate of change of the helix gradient 19counter to the impact direction 8. The helix gradient 19 preferablyincreases between 0.5 degrees and 2 degrees for each degree that thehelix rib 12 winds around the drill bit axis 6.

The shank end 4 of the drill bit 1 in the example is designed for theuse of handheld manual power turning tools. The shank end 4 essentiallyhas a cylindrical shape with a diameter 26. The shank end 4 has twoclosed grooves 27 in which locking elements of the manual power tool canengage from the radial side and slide along the drill bit axis 6.Grooves 28 oriented along the drill bit axis 6 allow torque to beapplied by the manual power tool.

A manufacturing process of the sample drill bit 1 involves two,preferably immediately consecutive process steps. An initial coldreshaping process is used to reshape a blank 29 to form a semifinishedproduct 30 with longitudinal ribs 31 (FIG. 5 ). The longitudinal ribs 31created in this way are twisted into a helix 3 in a second coldreshaping process (FIG. 8 ). Subsequently, a drill bit head 2 isattached.

For example, a manufacturing process starts with a rod-shaped blank 29.The blank 29 has a simple cylindrical or convex prismatic shape. Thecross section preferably has a circular, slightly elliptical, or convexpolygonal shape, e.g., hexagonal, that is perpendicular to thelongitudinal axis 32 of the blank 29. The cross section is preferablyconstant along the entire length of the blank 29. The blank 29preferably has a cross-sectional area that is around the same or up to50% larger than the cross-sectional area of the helix 3. The length ofthe blank 29 is the same or up to 20% shorter than the length of thedrill bit 1 without the drill bit head 2, i.e., the total length of thehelix 3 and the shank end 4. The blank 29 is preferably made of alow-alloy steel.

The blank 29 is conveyed to a first roller stand and cold reshaped toform a semifinished product 30. FIG. 5 shows the original blank 29 onthe right and the semifinished product 30 produced from the blank 29 onthe left. The semifinished product 30 is divided up into a connected,restructured section 33 and a connected, star-shaped structured (star)section 34. In this context, restructured means unchanged by the processdescribed below in comparison to the original shape of the blank 29.Therefore, the restructured section 33 essentially continues to becylindrical or convex prismatic in form. The star-shaped structuredsection 34 can be obtained by means of the process described below. Thestar shape of the star-shaped structured section 34 refers to its crosssection (FIG. 6 ) perpendicular to its longitudinal axis 32. The crosssection has the shape of a star, preferably a regular star. A star is apolygon with alternating concave corners, i.e., an interior angle ofmore than 180 degrees, and convex corners (points), i.e., an interiorangle of less than 180 degrees. The corners are typically rounded orflattened here. The face of the semifinished product 30 that is formedby the restructured section 33 is referred to below as the front face35, and the face of the semifinished product 30 that is formed by thestar-shaped section 34 is referred to below as the back face 36.

The star-shaped section 34 of the semifinished product 30 has three ormore longitudinal ribs 31 plus longitudinal grooves 37 arranged betweenthe adjoining longitudinal ribs 31. The longitudinal ribs 31 and thelongitudinal grooves 37 extend parallel to the longitudinal axis 32 ofthe semifinished product 30. The star-shaped section 34 has a constantstar-shaped cross section along the longitudinal axis 32 of thesemifinished product 30 (shown enlarged in FIG. 6 )—except for a shorttransitional area leading to the unstructured section 33. Thelongitudinal ribs 31 and the longitudinal grooves 37 start at the frontface 36 of the semifinished product 30; therefore, the longitudinalgrooves 37 are open at the front face 36. The longitudinal ribs 31 aredistributed uniformly around the longitudinal axis 32. For example, thefour longitudinal ribs 31 are arranged at angular distances of 90degrees. The longitudinal ribs 31 in the example all have the sameradial dimension (height). In an arrangement with an even number oflongitudinal ribs, the longitudinal ribs of a pair of diametricallyopposed longitudinal ribs each have the same height; however, the heightof two circumferentially adjacent longitudinal ribs 31 may be different.The depth 38 of the longitudinal grooves 37 corresponds to the depth 23of the helix 3 that is being produced.

Preferably, the semifinished product 30 is longitudinally rolled. Aroller stand has multiple rollers 39 that roll parallel to thelongitudinal axis 32 of the blank 29. The rollers 39 rotate around therotary axes 40 perpendicular to the longitudinal axis 32. The rollers 39generate the longitudinal grooves 37 in the semifinished product 30 thatare parallel to the longitudinal axis 32. The material displaced duringrolling 39 forms a longitudinal rib 31 parallel to the longitudinal axis32 between each of the adjacent longitudinal grooves 37. Theunstructured section 33 of the blank 29 remains unchanged and forms thebasis for the shank end 4.

The blank 29 is cold reshaped to form the semifinished product 30. Theblank 29 is at room temperature when it is fed into the rollers 39. Theblank 29 may warm up somewhat due to the rolling process, but itstemperature remains well below the recrystallization temperature ofsteel. Typically, the rolling process 39 takes place at a temperature of10 degrees Centigrade (° C.) to 80° C. The surface of the structuredsection 34 is hardened through the cold reshaping and ends up with lessductility than the blank 29.

A sample roller stand has a roller 39 for each of the longitudinalgrooves 37, of which there are four here in this example. An alternativeroller stand can generate two longitudinal grooves at the same time andconsequently only has half as many rollers. The rollers 39 can bepositioned in such a way that the blank 29 can be inserted between therollers 39 up to a starting point without it being reshaped. The rollingprocess 39 for the longitudinal grooves 37 begins at the starting pointbetween the front face 35 and the back face 36 and runs in a rollingdirection 41 from the starting point to the back face 36. The section 33between the front face 35 and the starting point remains unstructured.The section 34 between the starting point and the back face 36 has astar-shaped structure. The rolling process 39 begins with the closedends of the longitudinal grooves 37 and ends with the open ends of thelongitudinal grooves 37. During the rolling process 39, the blank 29 ismoved through the rollers 39 counter to the rolling direction 41 inrelation to the roller stand.

The rollers 39 in the example have a circular segment 42 for reshapingthe blank 29 and a flat segment 43 along their circumference. Therollers 39 are oriented with the flat segments 43 facing the blank 29 inorder to insert the blank 29. The distance of the flat segments to thelongitudinal axis 32 is greater than half the diameter 44 (radius) ofthe blank 29 so that the blank 29 is inserted between the rollers 39along the longitudinal axis 32 without touching the rollers 39. Theblank 29 is positioned after the rollers 39 with the section 33 that isnot to be machined in the feed direction 41. The rollers 39 are engagedwith the blank 29 in order to reshape the blank 29 to form thesemifinished product 30. With the rollers 39 in the example, this occursby means of simple pivoting around the axis 32 of the rollers 39. Therollers 39 generate the longitudinal grooves 37 and the longitudinalribs 31. The rolling process continues until the semifinished product 30is ejected by the rollers 39, whereby the longitudinal grooves 37 formedare open at the front end 36 in the feed direction 41.

The rolling process 39 of the longitudinal grooves 37 can also be begunwith the back face 36, or the open end of the longitudinal grooves 37.The blank 29 is introduced in the rolling direction 41 and reshaped inthe process until the rollers 39 reach the section 33. The rollers 39are pivoted into the non-reshaping position, and the semifinishedproduct 30 is removed.

As an alternative to rolling, the longitudinal grooves can be producedin the blank by means of extrusion. A die has a funnel-shaped, taperedopening. The opening tapers down to a star-shaped cross section thatcorresponds to the complementary or inverse shape of the structuredsection of the semifinished product. The funnel shape of the die can becomplementary to the transitional area; preferably, the die is as longas the transitional area. A groove base preferably rises continuously inthe transitional area. The shape of the groove base can rise along theaxis with the shape of a circle segment or rectilinearly. The extrusionprocess takes place at room temperature.

The longitudinal grooves 37 and the longitudinal ribs 31 of thesemifinished product 30 are then twisted in a second tool stand. FIG. 8shows a schematic diagram of the semifinished product 30 while thesecond tool is shaping the helix 3 in the semifinished product 30. Thesecond tool has a (reshaping) die 48 (FIG. 9 ) followed by a(supporting) die 49 (FIG. 10 ) on the working axis 46 and along theworking direction 47.

The reshaping die 48 has its narrowest point along the working axis 32,which essentially corresponds to the negative shape of the star section34. The supporting die 49 preferably has a uniform, hollow cross sectionalong the working axis 46, which is the inverse shape of the starsection 34. The reshaping die 48 can be pivoted around the working axis46 in relation to the supporting die 49. In the basic position, thecross section at the narrowest point of the reshaping die 48 and thecross section of the supporting die 49 are oriented in the same angularposition; in other words, for a projection along the working direction47, the smallest hollow cross section of the reshaping die 48 fullycovers the hollow cross section of the supporting die 49. Diagram number50 on the reshaping die 48 and diagram number 51 on the supporting die49 indicate the angular position. In the basic position, the two diagramnumbers point to each other.

The two dies 48 and 49 are pivoted into the basic position. The starsection 34 of the semifinished product 30 is inserted into the reshapingdie 48 and the supporting die 49 until it is adjacent to theunstructured section 33 in the working direction 47. The semifinishedproduct 30 is not reshaped in the process. The reshaping die 48 can bearagainst the semifinished product 30 in the direction of rotation 52. Thesupporting die 49 can bear against the semifinished product 30 counterto the direction of rotation 52.

The twisting process begins near the unstructured section 33 of thesemifinished product 30 and continues in the direction of the back face36 of the semifinished product 30. The reshaping die 48 is pivoted inthe direction of rotation 52 in relation to the supporting die 49. Thesemifinished product 30 is twisted between the reshaping die 48 and thesupporting die 49, whereby the semifinished product 30 bears against thereshaping die 48 in the direction of rotation 52, and the semifinishedproduct 30 bears against the reshaping die 49 counter to the directionof rotation 52. The pivoting process is depicted based on diagramnumbers 50 and 51, which have now shifted. From the perspective of theworking direction 47, for example, the direction of rotation 52 iscounterclockwise in order to produce a helix 3 with the typicaldirection of rotation 5.

The star section 34 of the semifinished product 30 is pulled through thetwo dies 48 and 49 counter to the working direction 47. In the process,the two dies 48 and 49 retain a fixed axial distance. For example, thesupporting die 49 touches the reshaping die 48 at all times. In anotherarrangement, a fixed gap 53 is specified. As an alternative to pullingthe semifinished product 30, the two dies 48 and 49 can be moved inrelation to the surrounding space. The two dies 48 and 49 are pivotedwhile being pulled out as described above. The relative pivoting angle54 that the reshaping die 48 is pivoted around in relation to the basicposition can be constant. The pivoting angle 54 is not equal to zero andis at least great enough for the star section 34 to be plasticallyshaped between the reshaping die 48 and the supporting die 49. Asuitable pivoting angle 54 can depend on the steel used for thesemifinished product 30, the desired helix gradient 19, and the gap 53.For example, a suitable pivoting angle 54 ranges from 10 degrees to 90degrees, preferably less than 50 degrees, and preferably with the totalof the pivoting angle 54 and the desired helix gradient 19 between 80degrees and 100 degrees. The pivoting angle 54 can also be varied duringthe process of pulling out in order to implement a greater helixgradient 19 near the drill bit head 2, for example.

The semifinished product 30 is cold reshaped through the testingprocess. The semifinished product 30 is at around room temperature atthe beginning of the twisting process. The twisting process can warm upthe semifinished product 30, but its temperature remains well below therecrystallization temperature of steel. Typically, the twisting processtakes place at a temperature of 10 degrees Centigrade (° C.) to 80° C.

The rolling process 39 directly preceding the twisting process is also acold reshaping process that reduces the ductility of the surface.However, the twisting process is carried out directly with thecold-reshaped semifinished product 30 with the hardened surface.

The reshaping die 48 has a base body 55 in an arbitrary design, such ascylindrical (FIG. 9 ). A profiled cavity 56 extends along a die axis 57,such as the cylinder axis, from a front side 58 (FIG. 11 ) to a backside 59 (FIG. 12 ) of the base body 55. The reshaping die 48 is pushedonto the semifinished product 30 with its front side 58 facing the frontface 35 of the semifinished product 30 and its back side 59 facing theback face 36 of the semifinished product 30. The die axis 57 coincideswith the longitudinal axis 32 of the semifinished product 30.

The cavity 56 grows continuously larger moving from the front side 58 tothe direction of the back side 59, i.e., in the working direction 47.The front opening at the front side 58 has the narrowest hollow crosssection; the rear opening at the back side 59 has the largest hollowcross section. The front opening is star-shaped. The star shape largelycorresponds to the cross section of the star section 34 of thesemifinished product 30. The front opening is the inverse shape withrespect to the cross section through the longitudinal ribs 31 and thelongitudinal grooves 37. The cavity 56 has following interior surfaces60 that face towards the direction of rotation 52 and leading interiorsurfaces 61 that face away from the direction of rotation 52. The cavity56 with the four points 62 in the example has four following interiorsurfaces 60 and four leading interior surfaces 61, which follow eachother in alternation around the cavity 56. Looking from the direction ofrotation 52, the following interior surfaces 60 each end at the tips 62,while the leading interior surfaces 61 begin at the tips of thestar-shaped front opening (cf. FIG. 11 ).

The leading interior surfaces 56 are preferably parallel to the die axis57. The leading interior surfaces 56 are preferably the inverse shapewith respect to the exterior surfaces of the star section 34 of thesemifinished product 30 that face towards the direction of rotation 52.The semifinished product 30 can therefore bear flat against the leadinginterior surfaces 56 and be inserted along the die axis 57 while slidingalong the leading interior sections 56.

The following interior surfaces 55 rise helix-shaped from the front side58 in the direction of rotation 52. The following interior surfaces 55therefore move away from the opposite leading surfaces 56 in the workingdirection 47. In the direction of rotation 52, the following interiorsurfaces 55 can press against the helix ribs 12 of the helix 3 beingproduced. The following interior surfaces 60 have the same chirality(handedness) as the helix 3 being produced—preferably right-handed.

A longitudinal section through the cavity 56 along the die axis 57 andat level XIII-XIII is shown in FIG. 13 .

The base body 55 has ramps 63 projecting towards the die axis 57. Theramp 63 has a foot surface formed by the front side 58. A head surfaceparallel to the foot surface limits the ramp 63 at the back side 59. Thefoot surface is greater than the head surface. The ramp 63 tapers downcontinuously in the working direction 47. The leading interior surface61 borders the ramp 63 counter to the direction of rotation 52. Theleading interior surface 61 is preferably parallel to the die axis 57.The following interior surface 60 borders the ramp 63 in the directionof rotation 52. The ramp 63 drops in the direction of rotation 52. Theramp 63 is as high as the reshaping die 48 at its front end 64 in thedirection of rotation 52 and narrow at its back end 65 in the directionof rotation 52.

The ramps 63 are arranged at the same angular distances around the dieaxis 57, such as at angular distances of 90 degrees. The ramps 63 can beformed identically; in particular, the ramps 63 lying diametricallyacross the die axis 57 are identical. In one design, the ramps 63 canhave different radial dimensions; for example, their radial distancefrom the die axis 57 is different.

Diagram number 50 shows the angular orientation of a tip 62 of thestar-shaped cavity 56. The position of diagram number 50 is arbitrary,and the same is true of the position of the diagram number 50 directlyon the reshaping die 48. The angular orientation of the reshaping die 48and its cavity 56 are known to a control system for the tool.

The supporting die 49 has a base body 66 in an arbitrary design, such ascylindrical (FIG. 10 ). A profiled cavity 67 extends along a die axis68, such as the cylinder axis, from a front side 69 (FIG. 14 ) to a backside 70 of the base body 66. After the reshaping die 48, the supportingdie 49 is pushed onto the star section 34 of the semifinished product 30until it is adjoining the reshaping die 48. The reshaping die 48 bearsagainst the back side 59 of the reshaping die 48. The die axis 68 of thesupporting die 49 coincides with the longitudinal axis 32 of thesemifinished product 30. A back side 70 of the supporting die 49 facestowards the working direction 47.

The front side 69 and the back side 70 of the supporting die 49 areessentially the same. The profiled cavity 67 has a cross section thatremains the same along the die axis 68. The cross section isstar-shaped—shown in the example with four tips 71 here—and isessentially the inverse shape with respect to the process star section34 of the semifinished product 30. The cross section largely correspondsto the opening at the back side 59 of the reshaping die 48.

The cavity 67 is enclosed by interior surfaces 72, which face towardsthe direction of rotation 52, and interior surfaces 73, which face awayfrom the direction of rotation 52. The interior surfaces 72 and 73 areparallel to the die axis 68. The shape of the opposite surfaces 72 and73 can be mirror-inverted.

A longitudinal section through the cavity 67 is shown along the cutXV-XV in FIG. 15 .

Diagram number 51 shows the angular orientation of a tip 71 of thestar-shaped cavity 67. The position of diagram number 51 is arbitraryper se, and also the position of diagram number 51 directly onsupporting die 49. The angular orientation of the supporting die 49 andits cavity 67 are known to a control system for the tool.

The second tool stand has an axially movable gripper 74, the reshapingdie 48, and the supporting die 49 arranged on the working axis 46.

The gripper 74 holds the semifinished product 30 on the working axis 46.The gripper 74 can be moved back and forth along the working axis 46 bya drive 75. For example, the drive 75 is a pneumatic, hydraulic drive ora mechanical drive with a feed screw. The gripper 74 can pick up thesemifinished product 30 and insert it into the two dies 48 and 49largely without power. The gripper 74 has enough power to pull thesemifinished product 30 out of the dies 48 and 49 that are pivotedtowards each other. When pulling out the semifinished product 30, thegripper 74 can turn it in the direction of rotation 5 in order tosupport the twisting process by the reshaping die 48.

The rotary drive 76 turns while continuously pulling out the gripper 74in the direction of rotation 52. The speed of the rotary drive 76 iscoupled to the feed of the axial drive 75. The rotary drive 76 turns thesemifinished product 30 360 degrees one time while the feed advances thesemifinished product 30 by the multiple of the pitch 20 of the helix 3that corresponds to the number of the helix segments.

At least one of the two dies 48 and 49 can be pivoted around the workingaxis 46. For example, the reshaping die 48 is provided with a pivotingdrive 77.

The reshaping die 48 and the supporting die 49 can be positioned in thebasic position. For example, the dies 48 and 49, provided with diagramnumbers 50 and 51 show diagram numbers 50 and 51 in the basic positionin the same direction, e.g., illustrated show both diagram numbers 50and 51. The opening of the cavity 56 on the front side 58 of thereshaping die 48 and the opening of the cavity 67 on the front side 69of the supporting die 49 are oriented the same say. For example, theirtips 62 and 71 point in the same angular directions. With the dies 49 inthe example, the interior surfaces 60 of the reshaping die 48 that facetowards the direction of rotation 52 and the interior surfaces 72 thatface towards the direction of rotation 52 are flush.

The basic position is characterized by the relative angular orientationof the following interior surface 60 of the reshaping die 48 that facestowards the direction of rotation 52 and the interior surface 73 of thesupporting die 49 that faces away from the direction of rotation 52.These two opposite interior surfaces 60 and 73 are adjacent to a cavity67 that corresponds to the cross section through the longitudinal ribs31. The longitudinal rib 31 can therefore be inserted along the die axes57 and 68 between the two interior surfaces 60 and 73 without needingany power.

The reshaping die 48 can be pivoted from the basic position in relationto the supporting die 49 by a pivoting angle 54 in the direction ofrotation 52, whereby it is irrelevant whether the reshaping die 48 orthe supporting die 49 is pivoted in relation to the surrounding area.The pivoting process can be performed by means of a suitable pivotingdrive 77, which can produce the necessary torque for the twistingprocess. For example, the pivoting drive 77 applies force throughrecesses in the base body 55.

The pivoting angle 54 is equal to zero in the basic position. An exampleof the pivoting angle 54 is shown based on the two diagram numbers 50and 51. The pivoting angle 54 is greater than zero in a pivotedposition.

In the pivoted position, the cavity 67 bordered by the followinginterior surface 60 of the reshaping die 48 that faces towards thedirection of rotation 52 and the interior surfaces 73 of the supportingdie 49 that face away from the direction of rotation 52 is smaller thanthe cross section of the longitudinal rib 31. The part of thelongitudinal rib 31 lying in the reshaping die 48 is twisted by this inthe direction of rotation 52.

For example, a suitable pivoting angle 54 ranges between 10 degrees and90 degrees, preferably less than 50 degrees. The pivoting angle ispreferably varied while the two dies 48 and 49 are being pulled off thesemifinished product 30. The pivoting angle goes down to zero,particularly at the unstructured section 33 and the back end 36.

What is claimed is:
 1. A drill bit, comprising: a drill bit head, amulti-strand helix made up of three or more helix ribs, and a shank endalong a drill bit axis; wherein the multi-strand helix is made up of aconveyance area, an attachment area, a discharge area, a helix gradient,and a pitch, wherein the attachment area is disposed between the drillbit head and the conveyance area and wherein the discharge area isdisposed between the conveyance area and the shank end; wherein thehelix ribs extend parallel to the drill bit axis in the attachment areaand the discharge area; wherein the helix gradient constantly increasesin size in a direction of the drill bit head in the attachment area witha rate between 0.25 degrees and 2 degrees for every degree that thehelix ribs wind around the drill bit axis.
 2. The drill bit according toclaim 1, wherein a cross-section of the multi-strand helix is constantfrom the drill bit head to the discharge area.
 3. The drill bitaccording to claim 1, wherein the drill bit head has break-off edgesparallel to the drill bit axis.
 4. The drill bit according to claim 1,wherein the helix gradient increases in the impact direction in theconveyance area.
 5. The drill bit according to claim 4, wherein theconveyance area extends along more than 80% of a length of themulti-strand helix.
 6. The drill bit according to claim 1, wherein thehelix gradient constantly increases in size in a direction of the shankend in the discharge area with a rate between 0.25 degrees and 2 degreesfor every degree that the helix ribs wind around the drill bit axis. 7.The drill bit according to claim 1, wherein the drill bit head issoldered or welded onto a level end surface of the attachment area.